Single crystals of (p-ClC(6)H(4)NH(3))H(2)PO(4) are synthesized in water by interaction of H(3)PO(4) and (p-ClC(6)H(4)NH(2)). This compound crystallizes in the orthorhomic system with the Pbca space group. Its unit-cell parameters are a=9.724(3), b=7.861(1), c = 25.078(6) angstrom, V = 1917.1(6) angstrom(3) and Z = 8. The crystal structure has been solved and refined to R = 0.039, using 4298 independent reflections. The atomic arrangement can be described by inorganic layers parallel to ab plane, between which the organic cations are located. This compound exhibits a reversible phase transition at 403 K. The electrical conductivity measurements show that the (p-ClC(6)H(4)NH(3))H(2)PO(4) has a conductivity value which goes from sigma = 0.88 x 10(-6) Omega(-1) cm(-1) at room tempearture (293 K) to 3.31 X 10(-4) Omega(-1) cm(-1) at 433 K. Its characterisation by TA, NMR and IR is reported too. (c) 2008 Elsevier Ltd. All rights reserved.